chore: add files cache for reading template tar archives from db (#17141)

coderd/files/cache_internal_test.go

@@ -0,0 +1,104 @@
+package files
+
+import (
+	"context"
+	"io/fs"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sync/errgroup"
+
+	"github.com/coder/coder/v2/testutil"
+)
+
+func TestConcurrency(t *testing.T) {
+	t.Parallel()
+
+	emptyFS := afero.NewIOFS(afero.NewReadOnlyFs(afero.NewMemMapFs()))
+	var fetches atomic.Int64
+	c := newTestCache(func(_ context.Context, _ uuid.UUID) (fs.FS, error) {
+		fetches.Add(1)
+		// Wait long enough before returning to make sure that all of the goroutines
+		// will be waiting in line, ensuring that no one duplicated a fetch.
+		time.Sleep(testutil.IntervalMedium)
+		return emptyFS, nil
+	})
+
+	batches := 1000
+	groups := make([]*errgroup.Group, 0, batches)
+	for range batches {
+		groups = append(groups, new(errgroup.Group))
+	}
+
+	// Call Acquire with a unique ID per batch, many times per batch, with many
+	// batches all in parallel. This is pretty much the worst-case scenario:
+	// thousands of concurrent reads, with both warm and cold loads happening.
+	batchSize := 10
+	for _, g := range groups {
+		id := uuid.New()
+		for range batchSize {
+			g.Go(func() error {
+				// We don't bother to Release these references because the Cache will be
+				// released at the end of the test anyway.
+				_, err := c.Acquire(t.Context(), id)
+				return err
+			})
+		}
+	}
+
+	for _, g := range groups {
+		require.NoError(t, g.Wait())
+	}
+	require.Equal(t, int64(batches), fetches.Load())
+}
+
+func TestRelease(t *testing.T) {
+	t.Parallel()
+
+	emptyFS := afero.NewIOFS(afero.NewReadOnlyFs(afero.NewMemMapFs()))
+	c := newTestCache(func(_ context.Context, _ uuid.UUID) (fs.FS, error) {
+		return emptyFS, nil
+	})
+
+	batches := 100
+	ids := make([]uuid.UUID, 0, batches)
+	for range batches {
+		ids = append(ids, uuid.New())
+	}
+
+	// Acquire a bunch of references
+	batchSize := 10
+	for _, id := range ids {
+		for range batchSize {
+			it, err := c.Acquire(t.Context(), id)
+			require.NoError(t, err)
+			require.Equal(t, emptyFS, it)
+		}
+	}
+
+	// Make sure cache is fully loaded
+	require.Equal(t, len(c.data), batches)
+
+	// Now release all of the references
+	for _, id := range ids {
+		for range batchSize {
+			c.Release(id)
+		}
+	}
+
+	// ...and make sure that the cache has emptied itself.
+	require.Equal(t, len(c.data), 0)
+}
+
+func newTestCache(fetcher func(context.Context, uuid.UUID) (fs.FS, error)) Cache {
+	return Cache{
+		lock:    sync.Mutex{},
+		data:    make(map[uuid.UUID]*cacheEntry),
+		fetcher: fetcher,
+	}
+}